The present invention relates generally to semiconductors and fabrication methods, and more particularly, to thin solar cell structures and a method of fabricating same.
The current technology for producing thin solar cells utilizes wet chemical etching to reduce the thickness of solar cell wafers (Si, III-V and II-VI) from about 0.007 inches thick down to approximately 0.0025 to 0.0035 inches thick. However, preferential chemical etching can open up lineages (line detects) in the wafer that leads to wafer breakage. Also, after the planar etching process, there is high attrition during subsequent cell manufacturing process steps and later during circuit assembly and panel bonding processes. It is also very difficult to attach silver interconnects to thin solar cells made by chemical etching procedures by welding processes, and almost impossible to weld Kovar or molybdenum interconnects thereto due to the high pressure required. Welded Kovar interconnects are known industry-wide to have high fatigue resistance for long term and extreme environment missions, and are therefore a preferred interconnect structure.
Satellite solar panel designers are continually striving to design high efficiency panels having low mass because of expensive satellite launch costs. Current satellite design goals place a premium on high power, and consequently there is a push for high efficiency solar panel technology. This makes GaAs and other III-V or II-VI type solar cells an attractive alternative to traditional Si solar cells. High efficiency solar cell substrates such as GaAs or Ge unfortunately have more than twice the mass penalty as Si-based solar cells and therefore must be substantially thinned to surpass the power per weight value of Si. This thinning results in high efficiency solar cells that are extremely fragile not only during cell and panel fabrication, but also throughout their life in the stressful space environment.
Accordingly, it is an objective of the present invention to provide for thin solar cell structures and a method of fabricating them that overcomes the limitations of conventional thin solar cells.